Session timeout in Web

Question

Dear friends,

My ASP.Net site works perfectly in local network. But after uploading in the net, session times out frequently.
I have 2 session variable.One is declared ( CompanyTitle) at Global.asax(Session_Start event), another in login page ( userName). The session variable declared in Global.asax is available in all pages, the other variable is not. It gives an error as "Object variable is not set to an instance.....". After that I declared this variable in Global.asax(Session_Start event) with "" as its default value. Now the problem is that the UserName session variable is reset into "" frequently.

my session entry in web.config is as
<sessionState mode="InProc" cookieless="UseCookies" timeout="60" >

Please advice me on this problem.